Vertical stacks of light emitting diodes and control transistors and method of making thereof

ABSTRACT

A light emitting device includes a vertical stack of a light emitting diode and a field effect transistor that controls the light emitting diode. An isolation layer is present between the light emitting diode and the field effect transistor, and an electrically conductive path electrically shorts a node of the light emitting diode to a node of the field effect transistor. The field effect transistor may include an indium gallium zinc oxide (IGZO) channel and may be located over the isolation layer. Alternatively, the field effect transistor may be a high-electron-mobility transistor (HEMT) including an epitaxial semiconductor channel layer and the light emitting diode may be located over the HEMT.

FIELD

The embodiments of the invention are directed generally to verticalstacks of light emitting diodes and control transistors and a method ofmanufacturing the same.

BACKGROUND

Light emitting devices such as light emitting diodes (LEDs) are used inelectronic displays, augmented reality displays, virtual realitydisplays, heads up displays, liquid crystal displays in laptops or LEDtelevisions, and direct displays. Light emitting devices include lightemitting diodes (LEDs) and various other types of electronic devicesconfigured to emit light. Generally, the manufacturing process for thevarious LED-containing displays employ a transfer process in which lightemitting diode dies are transferred to a backplane that includes anarray of control transistors. The transfer process for the lightemitting diode dies can employ bonding of individual light emittingdiode dies. The transfer processes for the light emitting diode diestend to be time consuming and expensive, and are prone to generation ofdefective devices. A more reliable and inexpensive method of providingcontrol transistors for an array of light emitting diodes is desired.

SUMMARY

According to an aspect of the present disclosure, a light emittingdevice is provided, which comprises: an epitaxial substrate; a lightemitting diode comprising an n-doped semiconductor material layer, alight-emitting active region, and a p-doped semiconductor materiallayer, in which the light-emitting active region comprises an epitaxialsemiconductor material in epitaxial alignment with the epitaxialsubstrate; at least one dielectric isolation layer overlying the lightemitting diode; a field effect transistor located over the dielectricisolation layer and comprising an indium gallium zinc oxide (IGZO)channel; and an electrically conductive path that electrically shorts anode of the light emitting diode to a node of the field effecttransistor.

According to another aspect of the present disclosure, a light emittingdevice is provided, which comprises: an epitaxial substrate; ahigh-electron-mobility transistor (HEMT) comprising an epitaxialsemiconductor channel layer and located on the epitaxial substrate; atleast one isolation layer located over the HEMT; a light emitting diodecomprising an n-doped semiconductor material layer, a light-emittingactive region, and a p-doped semiconductor material layer, wherein thelight-emitting active region comprises an epitaxial semiconductormaterial in epitaxial alignment with the at least one isolation layer;and an electrically conductive path that electrically shorts a node ofthe light emitting diode to a node of the HEMT.

According to another aspect of the present disclosure, a method offorming a light emitting device is provided, which comprises: forming alight emitting diode comprising an n-doped semiconductor material layer,a light-emitting active region, and a p-doped semiconductor materiallayer over an epitaxial substrate, wherein the light-emitting activeregion comprises an epitaxial semiconductor material in epitaxialalignment with the epitaxial substrate; forming at least one dielectricisolation layer over the light emitting diode; forming a field effecttransistor comprising an indium gallium zinc oxide (IGZO) channel andover the dielectric isolation layer; and forming an electricallyconductive path that electrically shorts a node of the light emittingdiode to a node of the field effect transistor.

According to another aspect of the present disclosure, a method offorming a light emitting device is provided, which comprises: forming ahigh-electron-mobility transistor (HEMT) comprising an epitaxialsemiconductor channel layer and on an epitaxial substrate; forming atleast one isolation layer over the HEMT, wherein the at least oneepitaxial dielectric isolation layer comprises an epitaxial dielectricmaterial in epitaxial alignment with the epitaxial semiconductor channellayer; forming a light emitting diode comprising an n-dopedsemiconductor material layer, a light-emitting active region, and ap-doped semiconductor material layer over the at least one epitaxialdielectric isolation layer, wherein the light-emitting active regioncomprises an epitaxial semiconductor material in epitaxial alignmentwith the at least one epitaxial dielectric isolation layer; and formingan electrically conductive path comprising a contact via structure thatextends through the at least one epitaxial dielectric isolation layer,wherein the electrically conductive path electrically shorts a node ofthe light emitting diode to a node of the HEMT.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic vertical cross-sectional view of a firstexemplary structure after formation of light emitting diodes accordingto a first embodiment of the present disclosure.

FIG. 1B is a magnified vertical cross-sectional view of a firstconfiguration for a light emitting diode of the first exemplarystructure of FIG. 1A.

FIG. 1C is a magnified vertical cross-sectional view of a secondconfiguration for a light emitting diode of the first exemplarystructure of FIG. 1A.

FIG. 1D is a magnified vertical cross-sectional view of a thirdconfiguration for a light emitting diode of the first exemplarystructure of FIG. 1A.

FIG. 1E is another magnified vertical cross-sectional view of a regionof a nanowire in the third configuration for a light emitting diode ofthe first exemplary structure of FIG. 1A.

FIG. 2 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of at least one dielectric isolationlayer and an indium gallium zinc oxide (IGZO) layer according to thefirst embodiment of the present disclosure.

FIG. 3 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of IGZO channels and a gatedielectric according to the first embodiment of the present disclosure.

FIG. 4 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of gate electrodes, sourceelectrodes, and drain electrodes according to the first embodiment ofthe present disclosure.

FIG. 5 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of metal interconnect structures andinterconnect-level dielectric layers according to the first embodimentof the present disclosure.

FIG. 6 is a schematic vertical cross-sectional view of an alternativeconfiguration of the first exemplary structure after formation of gateelectrodes and a gate dielectric layer according to the first embodimentof the present disclosure.

FIG. 7 is a schematic vertical cross-sectional view of the alternativeembodiment of the first exemplary structure after formation of metalinterconnect structures and interconnect-level dielectric layersaccording to the first embodiment of the present disclosure.

FIG. 8 is a schematic vertical cross-sectional view of a secondexemplary structure after formation of a high-electron-mobilitytransistor (HEMT) body layer stack according to a second embodiment ofthe present disclosure.

FIG. 9 is a schematic vertical cross-sectional view of the secondexemplary structure after formation of gate electrodes, sourceelectrodes, and drain electrodes for HEMT devices according to thesecond embodiment of the present disclosure.

FIG. 10 is a schematic vertical cross-sectional view of the secondexemplary structure after formation of an isolation layer stackaccording to the second embodiment of the present disclosure.

FIG. 11 is a schematic vertical cross-sectional view of the secondexemplary structure after formation of light emitting diodes accordingto the second embodiment of the present disclosure.

FIG. 12A is a schematic vertical cross-sectional view of the secondexemplary structure after formation of metal interconnect structures andinterconnect-level dielectric layers according to the second embodimentof the present disclosure.

FIG. 12B is a magnified vertical cross-sectional view of the lightemitting device of the second exemplary structure of FIG. 12A.

DETAILED DESCRIPTION

As stated above, the present disclosure is directed to vertical stacksof light emitting diodes and control transistors and a method ofmanufacturing the same, the various aspects of which are describedbelow. Throughout the drawings, like elements are described by the samereference numeral. The drawings are not drawn to scale. Multipleinstances of an element may be duplicated where a single instance of theelement is illustrated, unless absence of duplication of elements isexpressly described or clearly indicated otherwise. Elements with thesame reference numerals are presumed to have the same composition and/orcomponents unless expressly stated otherwise. Ordinals such as “first,”“second,” and “third” are employed merely to identify similar elements,and different ordinals may be employed across the specification and theclaims of the instant disclosure. Elements with a same reference numeralare presumed to have a same composition and to have a same thicknessrange, if applicable, unless expressly disclosed otherwise.

As used herein, a “light emitting device” refers to any device that isconfigured to emit light and includes any electronic device that isconfigured to emit light upon application of a suitable electrical bias.A light emitting device may include at least one light emitting diode(LED) that is electrically coupled to at least one control device suchas at least one transistor. A light emitting device may include avertical structure (e.g., a vertical LED) in which the p-side and n-sidecontacts are located on opposite sides of the structure or a lateralstructure in which the p-side and n-side contacts are located on thesame side of the structure.

Referring to FIGS. 1A-1E, various configurations of a first exemplarystructure according to a first embodiment of the present disclosure areillustrated after formation of light emitting diodes 20. FIG. 1A is aschematic vertical cross-sectional view of the first exemplarystructure. FIG. 1B is a magnified vertical cross-sectional view for afirst configuration of the first exemplary structure. FIG. 1C is amagnified vertical cross-sectional view for a second configuration ofthe first exemplary structure. FIG. 1D is a magnified verticalcross-sectional view of a third configuration of the first exemplarystructure. FIG. 1E is another magnified vertical cross-sectional view ofthe third configuration of the first exemplary structure at a highermagnification than the magnification of FIG. 1D.

The first exemplary structure includes a substrate 10. In oneembodiment, the substrate 10 can be a single crystalline substrate onwhich a III-V compound semiconductor material can be epitaxiallydeposited. For example, the substrate 10 can be a sapphire (aluminumoxide) layer having a c-plane (0001 plane) as the crystallographic planeof the top surface.

Light emitting diodes 20 are formed on a top surface of the substrate10. In the first configuration illustrated in FIGS. 1B and 1 n thesecond configuration illustrated in FIG. 1C, the substrate 10 can be anepitaxial substrate 10, and the light emitting diodes 20 can include asingle crystalline n-doped gallium nitride layer 804 that includes asingle crystalline gallium nitride material in epitaxial alignment withthe crystalline structure of the substrate 10. The single crystallinen-doped gallium nitride layer 804 can be formed, for example, by anepitaxial deposition process such as metal-organic chemical vapordeposition (MOCVD) process. The thickness of the single crystallinen-doped gallium nitride layer 804 can be selected such that dislocationdefects caused by lattice mismatch between the lattice parameters of thesubstrate 10 and gallium nitride are healed, and the defect densitydecreases to a level suitable for device fabrication at the top surfaceof the single crystalline n-doped gallium nitride layer 804. Forexample, the thickness of the single crystalline n-doped gallium nitridelayer 804 can be in a range from 1.2 microns to 6 microns, althoughlesser and greater thicknesses can also be employed. The singlecrystalline n-doped gallium nitride layer 804 may be doped withelectrical dopants of a first conductivity type. For example, the singlecrystalline n-doped gallium nitride layer 804 may be n-doped byintroduction of silicon as n-type dopants during the epitaxialdeposition process.

In some configurations such as the first and second configurationsillustrated in FIGS. 1B and 1C, the light emitting diodes include aplanar layer stack (1110, 1118, 1120, 1130, 1140, 1150, 1160) that isformed on the single crystalline n-doped gallium nitride layer 804. Theplanar layer stack (1110, 1118, 1120, 1130, 1140, 1150, 1160) caninclude an epitaxial material layer stack (i.e., a stack of epitaxialmaterial layers that are epitaxially aligned among one another) thatincludes, in order, one or more of planar superlattice structures (1110,1120) comprising respective strain-modulating layer stacks (1112, 1114)and/or (1112, 1124), a planar light-emitting quantum well that includesa planar light-emitting indium gallium nitride layer 1132 and a planarGaN barrier layer 1134, and a planar p-doped III-nitride layer 1140,which is preferably a p-doped aluminum gallium nitride layer. However,the p-doped III-nitride layer 1140 may alternatively comprise galliumnitride or indium aluminum gallium nitride with a low indium content.The plurality of planar superlattice structures (1110, 1120) canmodulate and reduce the strain of the planar light-emitting InGaN layer1132, thereby enabling high indium incorporation with low defectformation and thus enabling high emission efficiency across the redwavelength range. The planar light-emitting indium gallium nitride layer1132 may be configured to emit light at a first peak wavelength in arange from 600 nm to 750 nm under electrical bias thereacross. In oneembodiment, the first peak wavelength can be in a range from 610 nm to680 nm.

In an illustrative example, the plurality of strain-modulating layerstacks can include first strain-modulating layer stacks (1112, 1114) andsecond strain-modulating layer stacks (1122, 1124). Each firststrain-modulating layer stack (1112, 1114) can include a firstintervening indium gallium nitride layer 1112 and a first interveningGaN layer 1114. Each second strain-modulating layer stack (1122, 1124)can include a second intervening indium gallium nitride layer 1122 and asecond intervening GaN layer 1124. In an alternative embodiment, atleast one layer among the first intervening GaN layers 1114 and thesecond intervening GaN layers 1124 may be replaced with a respectiveintervening aluminum gallium nitride layer or indium gallium nitridelayer having a different indium concentration than the first interveningindium gallium nitride layers 1112 or the second intervening indiumgallium nitride layers 1122 within the respective strain-modulatinglayer stack.

In one embodiment, the first intervening indium gallium nitride layers1112 can have a lower indium concentration than the second interveningindium gallium nitride layers 1122. For example, the first interveningindium gallium nitride layers 1112 can have a composition ofIn_(p)Ga_((1-p))N in which p is in a range from 0.04 to 0.08, althoughlesser and greater values for p can also be employed. The secondintervening indium gallium nitride layers 1122 can have a composition ofIn_(q)Ga_((1-q))N in which q is in a range from 0.08 to 0.12, althoughlesser and greater values for q can also be employed.

The first strain-modulating layer stacks (1112, 1114) containing thelower indium concentration first intervening indium gallium nitridelayers 1112 can be considered as “UV” stacks (e.g., which would emit UVradiation having a peak wavelength less than 400 nm). The secondstrain-modulating layer stacks (1122, 1124) containing the higher indiumconcentration second intervening indium gallium nitride layers 1122 canbe considered as “blue” stacks (e.g., which would emit blue visiblelight having a peak wavelength between 400 nm and 495 nm).

The thickness of each first intervening indium gallium nitride layer1112 can be in a range from 0.7 nm to 1.5 nm, although lesser andgreater thicknesses can also be employed. The thickness of each firstintervening GaN layer 1114 can be in a range from 3 nm to 6 nm, althoughlesser and greater thicknesses can also be employed. The thickness ofeach second intervening indium gallium nitride layer 1122 can be in arange from 2 nm to 3 nm, although lesser and greater thicknesses canalso be employed. The thickness of each second intervening GaN layer1124 can be in a range from 15 nm to 20 nm, although lesser and greaterthicknesses can also be employed.

The layers of the first and the second superlattice structures (1110,1120) may be not intentionally doped with p-type or n-type dopants. SuchIII-nitride layers that are not intentionally doped typically haven-type conductivity.

Without wishing to be bound by any particular theory, it is believedthat it is possible that the effective lattice constant of the secondsuperlattice structure 1120 is greater than the effective latticeconstant of the first superlattice structure 1110 due to the indiumcontent of the second intervening indium gallium nitride layers 1122 inthe second strain-modulating layer stacks (1122, 1124) of the secondsuperlattice structure 1120 being higher than the indium content of thefirst intervening indium gallium nitride layers 1112 in the secondstrain-modulating layer stacks (1122, 1124) of the first superlatticestructure 1110.

The first superlattice structure 1110 can include 3 to 30, such as 10 to15, first strain-modulating layer stacks (1112, 1114), although lesserand greater number of repetitions can also be employed. The totalthickness of the first multi quantum well structure 1110 can be in arange from 20 nm to 150 nm, although lesser and greater thicknesses canalso be employed.

The second superlattice structure 1120 can include 2 to 15, such as 5 to10, second strain-modulating layer stacks (1122, 1124), although lesserand greater number of repetitions can also be employed. The totalthickness of the second superlattice structure 1120 can be in a rangefrom 20 nm to 150 nm, although lesser and greater thicknesses can alsobe employed. The second superlattice structure 1120 can include a lowernumber of strain-modulating layer stacks (i.e., a lower number oflayers) than the first superlattice structure 1110.

Each strain-modulating layer stack (1112, 1114) or (1122, 1124) canfunction as buffer layers that provide strain accommodation between twolayers that are located on opposite sides of the strain-modulating layerstack in the respective superlattice structure (1110, 1120). Forexample, the difference in the lattice parameters of the singlecrystalline n-doped gallium nitride layer 804 and the planarlight-emitting indium gallium nitride layer 1132 can be accommodated bythe strain-modulating layer stacks which provide gradual transition oflattice parameters between the single crystalline n-doped galliumnitride layer 804 and the planar light-emitting indium gallium nitridelayer 1132 so that the planar light-emitting indium gallium nitridelayer 1132 can be formed as a high quality epitaxial film. Thesuperlattice structures (1110, 1120) stop lattice defects, such asdislocations and other defects from propagating from the substrate orunderlying layer 804 into the light emitting region 1130 (i.e., activeregion) containing the planar light-emitting indium gallium nitridelayer 1132.

It is noted that the indium gallium nitride and gallium nitride layersin the plurality of strain-modulating layer stacks (1112, 1114) or(1122, 1124) have respective Wurtzite structures. As used herein, an“effective lattice constant” of a layer stack having a Wurtzitestructure is the weighted average of hexagonal-plane lattice constants“a” of the Wurtzite structures of all component layers within the layerstack in which each lattice constant “a” is weighted by the fractiondefined by the number of all atoms within the respective component layerdivided by the number of all atoms within the layer stack.

In one embodiment, the effective lattice parameter and the atomicconcentration of indium in the intervening indium gallium nitride layers(1112, 1122) of the plurality of strain-modulating layer stacks (1112,1114) or (1122, 1124) can monotonically increase with the physicaldistance of each strain-modulating layer stack (1112, 1114) or (1122,1124) from the single crystalline n-doped GaN portion, i.e., from thesingle crystalline n-doped gallium nitride layer 804. Thus, the bottomfirst intervening indium gallium nitride layer 1112 in the firstsuperlattice 1110 may have a lower indium content and a lower latticeparameter than the top first intervening indium gallium nitride layer1112 in the first superlattice 1110. Alternatively, all firstintervening indium gallium nitride layers 1112 in the first superlattice1110 may have about the same indium content and the same latticeparameter.

Likewise, in one embodiment, the bottom second intervening indiumgallium nitride layer 1122 in the second superlattice 1120 may have alower indium content and a lower lattice parameter than the top secondintervening indium gallium nitride layer 1122 in the second superlattice1120. Alternatively, all second intervening indium gallium nitridelayers 1122 in the second superlattice 1120 may have about the sameindium content and the same lattice parameter.

Optionally, a planar GaN spacer layer 1118 can be provided between thegroups of the first strain-modulating layer stacks (1112, 1114) of thefirst superlattice structure 1110 and the groups of the secondstrain-modulating layer stacks (1122, 1124) of the second superlatticestructure 1120 to reduce overall strain during the epitaxial growth ofthe layers. For example, the planar GaN spacer layer 1118 can have athickness in the range from 30 nm to 50 nm, although lesser and greaterthicknesses can also be employed. The planar GaN spacer layer 1118 maybe not intentionally doped with p-type or n-type dopants. Such GaN layerthat is not intentionally doped typically has n-type conductivity.

The light emitting region 1130 may comprise a planar light-emittingquantum well 1130. The planar light-emitting quantum well 1130 can beformed on the most distal strain-modulating layer stack, which can bethe most distal second strain-modulating layer stack (1122, 1124) withinthe second superlattice structure 1120. In the first configurationillustrated in FIG. 1B, the planar light-emitting quantum well 1130includes a planar light-emitting indium gallium nitride layer 1132, aplanar aluminum gallium nitride layer 1133, and a planar GaN barrierlayer 1134, in that order. In one embodiment, these layers are notintentionally doped.

The planar light-emitting indium gallium nitride layer 1132 includes anepitaxial indium gallium nitride material having a composition thatemits light at a peak wavelength in a range from 600 nm to 750 nm, andpreferably in a range from 610 nm to 680 nm. In one embodiment, theplanar light-emitting indium gallium nitride layer 1132 has acomposition of In_(x)Ga_((1-x))N, in which x is in a range from 0.26 to0.55 (i.e., higher indium content than underlying indium gallium nitridelayers 1112 and 1122). In an embodiment, the planar light-emittingindium gallium nitride layer 1132 can have a thickness in a range from 2nm to 5 nm.

The planar aluminum gallium nitride layer 1133 can have a composition ofAl_(y)Ga_((1-y))N, in which y is in a range from 0.3 to 1.0 (such asfrom 0.5 to 0.8). In an embodiment, the planar aluminum gallium nitridelayer can have a thickness in a range from 0.5 nm to 5.0 nm, such asfrom 0.5 nm to 1.0 nm. Without wishing to be bound by any particulartheory, it is believed that the planar aluminum gallium nitride layer1133 reduces or prevents evaporation of indium from the underlyingplanar light-emitting indium gallium nitride layer 1132 duringdeposition to provide a sufficiently high indium content in layer 1132to permit layer 1132 to emit visible light with a peak wavelength in thered color range (e.g., to emit red light). Additionally oralternatively, modification of band structure and piezoelectric effectsof the second superlattice structure 1120 may enable shifting the peakwavelength from the aluminum gallium nitride layer 1133 toward a longerwavelength, e.g., toward the red wavelength range from 610 nm to 680 nm.Further, the planar aluminum gallium nitride layer 1133 may providestrain compensation with the p-side layers 1140 and 1150 to providebetter quality (i.e., lower defect) p-side layers and/or may moderatethe quantum well band structure in the planar aluminum gallium nitridelayer 1132 due to an undesirable piezoelectric effect that separateselectrons and holes. The strain compensation can occur between thequantum well (that emits the red light) and the rest of the epitaxialstack, principally to reduce misfit defect formation in the active layeritself as well as in the p-layers.

The planar GaN barrier layer 1134 can have a thickness in a range from15 nm to 20 nm, although lesser and greater thicknesses can also beemployed. The planar GaN barrier layer 1134 provides an energy barrierbetween the planar light-emitting indium gallium nitride layer 1132 andp-type compound semiconductor material layers to be subsequently formed(e.g., to form a quantum well for light emission).

The various material layers within the first superlattice structure1110, the planar GaN spacer layer 1118, the second superlatticestructure 1120, and the planar light-emitting quantum well 1130 can be“undoped” and thus intrinsic (i.e., free of electrical dopants), or havea low concentration level of electrical dopants that is typically causedby incorporation of residual dopants in a reactor chamber. As usedherein, an “undoped” semiconductor material refers to a semiconductormaterial that has not been subjected to an intentional doping processduring fabrication. It is well known in the art that an undopedsemiconductor material typically has a free charge carrier concentrationthis is insufficient to render the semiconductor material conductive.Typically, an undoped semiconductor material has a free charge carrierconcentration not greater than 1.0×10¹⁶/cm³.

The second configuration of the first exemplary structure illustrated inFIG. 1C can be derived from the planar material layer stack in the firstconfiguration of the first exemplary structure of FIG. 1B by modifyingthe light emitting region 1130 to include multiple planar light-emittingquantum wells (i.e., to include two repetitions of a light-emittingindium gallium nitride layer 1132, a planar aluminum gallium nitridelayer 1133, and a GaN barrier layer 1134). Thus, the light emittingregion 1130 of the second exemplary planar material layer stack includesa stack, from a proximal side to the planar single crystalline n-dopedGaN layer 804 to a distal side from the planar single crystallinen-doped GaN layer 804, a light-emitting indium gallium nitride layer1132, a planar aluminum gallium nitride layer 1133, a GaN barrier layer1134, an additional light-emitting indium gallium nitride layer 1132located on the GaN barrier layer 1134, an addition planar aluminumgallium nitride layer 1133, and an additional GaN barrier layer 1134located on the additional light-emitting indium gallium nitride layer1133. The p-doped aluminum gallium nitride layer 1140 can be formeddirectly on the additional GaN barrier layer 1134.

A planar p-doped III-nitride layer, such as p-doped aluminum galliumnitride layer 1140 can be formed on the planar light-emitting quantumwell 1130 of the first or second configuration of the first exemplarystructure. For example, the planar p-doped aluminum gallium nitridelayer 1140 can be formed directly on the planar GaN barrier layer 1134.In an embodiment, the planar p-doped aluminum gallium nitride layer 1140can have a thickness in a range from 10 nm to 20 nm, although lesser andgreater thicknesses can also be employed. In an embodiment, the planarp-doped aluminum gallium nitride layer 1140 can be p-doped at a dopantconcentration that provides a free charge carrier concentration (i.e.,the concentration of holes) in a range from 1.0×10¹⁷/cm³ to3.0×10²⁰/cm³, such as from 3.0×10¹⁷/cm³ to 1.0×10²⁰/cm³, although lesserand greater free charge carrier concentrations can also be employed. Theplanar p-doped aluminum gallium nitride layer 1140 can have a loweraluminum contact than the aluminum gallium nitride layer 1133. Forexample, the planar p-doped aluminum gallium nitride layer 1140 can havea composition Al_(z)Ga_((1-z))N, in which z is less than 0.5, such as ina range from 0.2 to 0.3.

An optional first p-doped compound semiconductor material layer 1150 canbe formed on the planar p-doped aluminum gallium nitride layer 1140. Thefirst p-doped compound semiconductor material layer 1150 can include ap-doped single crystalline compound semiconductor material such asp-doped gallium nitride. In one embodiment, the first p-doped compoundsemiconductor material layer 1150 can be p-doped at a dopantconcentration that provides a free charge carrier concentration (i.e.,the concentration of holes) in a range from 1.0×10¹⁷/cm³ to3.0×10²⁰/cm³, such as from 3.0×10¹⁷/cm³ to 1.0×10²⁰/cm³, although lesserand greater free charge carrier concentrations can also be employed.

A second p-doped compound semiconductor material layer 1160 can beformed on the first p-doped compound semiconductor material layer 1150.The second p-doped compound semiconductor material layer 1160 caninclude a heavily p-doped single crystalline compound semiconductormaterial such as p-doped gallium nitride. The dopant concentration inthe second p-doped compound semiconductor material layer 1160 can begreater than the dopant concentration in the first p-doped compoundsemiconductor material layer 1150. In one embodiment, the second p-dopedcompound semiconductor material layer 1160 can be heavily p-doped at adopant concentration that provides a free charge carrier concentration(i.e., the concentration of holes) in a range from 5.0×10¹⁹/cm³ to3.0×10²¹/cm³, such as from 1.0×10²⁰/cm³ to 2.0×10²¹/cm³, although lesserand greater free charge carrier concentrations can also be employed. Thetotal thickness of the first and second p-doped compound semiconductormaterial layers (1150, 1160) can be in a range from 90 nm to 200 nm,although lesser and greater thicknesses can also be employed.

Top electrodes 30 can be formed on the light emitting diodes 20. Thearea of each light emitting diode 20 can be defined by the area of arespective one of the top electrodes 20. In one embodiment, each topelectrode 30 can include a vertical stack of a transparent conductiveelectrode and a patterned portion of a reflector layer 966.

The transparent conductive electrodes can be formed by depositing andpatterning a transparent conductive oxide layer 964 over the first andsecond p-doped compound semiconductor material layers (1150, 1160). Incase light emitted from the light-emitting indium gallium nitride layer1132 is directed downward toward the single crystalline n-doped galliumnitride layer 804 by a reflector layer to be subsequently formed abovethe transparent conductive electrode, then the transparent conductiveoxide layer 964 is herein referred to a backside transparent conductiveoxide layer 964. The transparent conductive oxide layer 964 includes atransparent conductive oxide material such as indium tin oxide oraluminum doped zinc oxide. The transparent conductive oxide layer 964can be deposited as a continuous material layer that extends across theentire area of the p-doped compound semiconductor material layer 812.The thickness of the transparent conductive oxide layer 964 can be in arange from 100 nm to 2 microns, such as from 200 nm to 1 micron,although lesser and greater thicknesses can also be employed.

Optionally, a reflector material can be deposited to form a reflectorlayer 966 that continuously extends over the backside transparentconductive oxide layer 964. The reflector layer 966 is electricallyshorted to the p-doped compound semiconductor material layer 1160through the backside transparent conductive oxide layer 964. In oneembodiment, the reflector layer 966 includes at least one materialselected from silver, aluminum, copper, and gold. In one embodiment, thereflector material can be deposited by physical vapor deposition(sputtering) or vacuum evaporation. The reflector layer 966 can beemployed to reflect light emitted from the active region 1130 throughthe transparent substrate 10. In case the reflector layer 966 isdeposited and patterned to be incorporated into top electrodes (964,966), the area of each patterned portion of the reflector layer 966defines the areas of a respective light emitting diode. Each lightemitting diode 20 can be in a downward-emitting configuration, i.e., aconfiguration in which light exits the light emitting diodes through thesubstrate 10, which can include a transparent material such as sapphire.

While exemplary configurations of planar light emitting diodes arepresented in the drawings for illustrative purposes, the presentinvention can be practiced with any other planar light emitting diodesthat are formed on a substrate 10.

Other types of light emitting diodes 20 can be formed on the substrate10 in lieu of, or in addition to, the light emitting diodes 20 in thefirst or second configuration. FIGS. 1D and 1E illustrate a thirdconfiguration of the first exemplary structure that includes non-planardiodes, i.e., diodes including non-planar structures therein.

In the third configuration of the exemplary structure, the lightemitting diodes 20 can include an optional epitaxial buffersemiconductor layer 24 and a planar single crystalline n-doped GaN layer26 that are formed on the substrate 10. The planar single crystallinen-doped GaN layer 26 functions as one node of each light emitting diodeto be subsequently formed. The substrate 10 can be an epitaxialsubstrate, and the optional epitaxial buffer semiconductor layer 24 andthe planar single crystalline n-doped GaN layer 26 can be formed by anepitaxial deposition process so that each of the epitaxial buffersemiconductor layer 24 and the planar single crystalline n-doped GaNlayer 26 includes a single crystalline semiconductor material that isepitaxially aligned to the single crystalline structure of the growthsubstrate 802 (which can include a single crystalline sapphire (Al₂O₃)substrate).

A growth mask 42 is subsequently formed on the top surface of the planarsingle crystalline n-doped GaN layer 26. The growth mask 42 includes adielectric material such as silicon nitride or silicon oxide, and can beformed, for example, by chemical vapor deposition. The thickness of thegrowth mask 42 can be in a range from 10 nm to 500 nm, although lesserand greater thicknesses can also be employed.

Openings are formed through the growth mask 42, for example, byapplication and patterning of a photoresist layer (not shown) and asubsequent etch process that etches physically exposed portions of thegrowth mask 42 employing the patterned photoresist layer as an etchmask. The photoresist layer can be subsequently removed, for example, byashing. The openings may be circular, elliptical, or polygonal. In anillustrative example, the maximum lateral dimension of each opening(such as a diameter or a major axis) may be in a range from 50 nm to 500nm, although lesser and greater maximum lateral dimensions can beemployed for each. The openings can form a two-dimensional array, whichmay be, for example, a hexagonal array (which includes an equilateraltriangular array), a rectangular array, or a parallelogram array. Thecenter-to-center distance between a neighboring pair of openings can bein a range from 150 nm to 5 microns, although lesser and greaterspacings can also be employed.

Nanowire cores 32 can be grown through the openings in the patternedgrowth mask 42 by a selective epitaxy process performed in a Group Vlimited regime. Alternatively, a silicon enriched growth CVD method, apulsed growth CVD method or an MBE method can be employed to form thenanowire cores 32. Each nanowire core 32 extends through a respectiveopening in the patterned growth mask 42 along a direction substantiallyperpendicular to the top surface of the substrate 802. The nanowirecores 32 can be grown from the physically exposed surfaces of the planarsingle crystalline n-doped GaN layer 26 by a selective epitaxy processunder process conditions that provide epitaxial growth of a singlecrystalline doped semiconductor material having a doping of the firstconductivity type (such as n-doped GaN) along the directionperpendicular to the c-plane. The c-plane can be parallel to the topsurface of the planar single crystalline n-doped GaN layer 26. Growth ofthe nanowire cores 32 can be performed by a selective semiconductordeposition process that grows a single crystalline semiconductormaterial from physically exposed semiconductor surfaces primarily alongthe c-direction, i.e., the direction perpendicular to the c-plane, whilenot growing any semiconductor material from dielectric surfaces. Theentirety of each nanowire core 32 can be single crystalline and inepitaxial alignment with the planar single crystalline n-doped GaN layer26.

As used herein, the aspect ratio of each nanowire core 32 is defined asthe final height of the nanowire core to the maximum lateral dimensionat the base of the nanowire core, which is the maximum lateral dimensionof the respective opening through the growth mask 42. The aspect ratioof the nanowire cores 32 can be in a range from 2 to 40, although lesserand greater aspect ratios can also be employed.

A shell layer stack 34 is formed on each nanowire cores 32, which is asingle crystalline n-doped GaN portion. FIG. 1E is a magnified view of aregion of the exemplary device structure of FIG. 1D. The growth mode canchange to a Group III limited growth mode, which is also referred to asa high V/III growth mode employed in conventional growth of III-Vmaterials, for formation of the shell layers within the shell layerstack 34. Thus, the shell layers can be formed on all physically exposedsemiconductor surfaces during the respective selective epitaxyprocesses.

The shell layer stack 34 can include an epitaxial shell layer stack(i.e., a stack of epitaxial shell layers that are epitaxially alignedamong one another) that includes, in order, an optional plurality ofshell strain-modulating layer stacks (1210, 1220, 1225), a shelllight-emitting quantum well that includes a shell light-emitting indiumgallium nitride layer 1232, a shell aluminum gallium nitride layer 1133,a shell GaN barrier layer 1234, and a shell p-doped aluminum galliumnitride layer 1240. The shell light-emitting indium gallium nitridelayer 1232 is configured to emit light at a first peak wavelength in arange from 600 nm to 750 nm under electrical bias thereacross. In oneembodiment, the first peak wavelength can be in a range from 610 nm to680 nm. As used herein, a “shell layer” refers to a continuous materiallayer that laterally encloses and overlies all facets of a nanowire core32. The thickness of a shell layer may vary across facets of thenanowire core 32. For example, vertical portions of a shell layer may bethicker than angled portions of the shell layer.

Each strain-modulating layer stack (1210, 1220, 1225) includes at leasta pair of layers that includes a respective intervening indium galliumnitride layer (1212, 1222, 1226) and a respective intervening GaN layer(1214, 1224, 1228). The inner most strain-modulating layer stack maycomprise a superlattice shell 1210 which contains a plurality of stacksof pairs of layers 1212 and 1214. Each strain-modulating layer stack(1210, 1220, 1225) can function as buffer layers that provide strainrelaxation between two layers that are located on opposite sides of thestrain-modulating layer stack (1210, 1220, 1225). For example, thedifference in the lattice parameters of the single crystalline n-dopedgallium nitride portion of the nanowire cores 32 and the shelllight-emitting indium gallium nitride layer 1232 can be accommodated bythe strain-modulating layer stack (1210, 1220, 1225), which providegradual transition of lattice parameters and trap lattice defectsbetween the nanowire core 32 and the shell light-emitting indium galliumnitride layer 1232 so that the shell light-emitting indium galliumnitride layer 1232 can be formed as a high quality epitaxial film.

The various layers in the plurality of shell strain-modulating layerstacks (1210, 1220, 1225) have respective Wurtzite structures. In anillustrative example, the plurality of strain-modulating layer stacks(1210, 1220, 1225) can include a superlattice shell 1210 of a plurality(e.g., five to ten) of first strain-modulating layer stacks (1212,1214), a second strain-modulating layer stack 1220, and a thirdstrain-modulating layer stack 1225. Each first strain-modulating layerstack (1212, 1214) can include a first intervening indium galliumnitride layer 1212 and a first intervening GaN layer 1214. The secondstrain-modulating layer stack 1220 can include a second interveningindium gallium nitride layer 1222 and a second intervening GaN layer1224. The third strain-modulating layer stack 1225 can include a thirdintervening indium gallium nitride layer 1226 and a third interveningGaN layer 1228.

Each of the first strain-modulating layer stacks (1212, 1214) can have afirst effective lattice constant, the second strain-modulating layerstack 1220 can have a second effective hexagonal-plane lattice constantthat is greater than the first effective hexagonal-plane latticeconstant, and the third strain-modulating layer stack 1225 can have athird effective hexagonal-plane lattice constant that is greater thanthe second effective hexagonal-plane lattice constant.

In one embodiment, the atomic concentration of indium in the interveningindium gallium nitride layers (1212, 1222, 1226) of the plurality ofstrain-modulating layer stacks (1210, 1220, 1225) can monotonicallyincrease with the physical distance of each strain-modulating layerstack (1210, 1220, 1225) from the single crystalline n-doped GaNportion, i.e., from the nanowire core 32.

In one embodiment, the first intervening indium gallium nitride layers1212 can have a lower indium concentration than the second interveningindium gallium nitride layer 1222. For example, the first interveningindium gallium nitride layers 1212 can have a composition ofIn_(p)Ga_((1-p))N in which p is in a range from 0.04 to 0.08, althoughlesser and greater values for p can also be employed. The secondintervening indium gallium nitride layer 1222 can have a composition ofIn_(q)Ga_((1-q))N in which p is in a range from 0.10 to 0.12, althoughlesser and greater values for q can also be employed. The thirdintervening indium gallium nitride layer 1226 can have a composition ofIn_(r)Ga_((1-r))N in which r is in a range from 0.15 to 0.30, althoughlesser and greater values for r can also be employed. The thickness ofeach first intervening indium gallium nitride layer 1212 can be in arange from 0.7 nm to 1.5 nm, although lesser and greater thicknesses canalso be employed. The thickness of each first intervening GaN layer 1214can be in a range from 3 nm to 5 nm, although lesser and greaterthicknesses can also be employed. The thickness of the secondintervening indium gallium nitride layer 1222 can be in a range from 4nm to 6 nm, although lesser and greater thicknesses can also beemployed. The thickness of the second intervening GaN layer 1224 can bein a range from 2 nm to 4 nm, although lesser and greater thicknessescan also be employed. The thickness of the third intervening indiumgallium nitride layer 1226 can be in a range from 2.5 nm to 8 nm,although lesser and greater thicknesses can also be employed. Thethickness of the third intervening GaN layer 1224 can be in a range from6 nm to 10 nm, although lesser and greater thicknesses can also beemployed.

Optionally, a shell GaN spacer layer 1218 can be provided between thegroups of the first strain-modulating layer stacks (1212, 1214) (i.e.,the superlattice shell 1210) and the second strain-modulating layerstack 1220 to reduce overall stress during the epitaxial growth of theshell layers. For example, the shell GaN spacer layer 1218 can have athickness in the range from 30 nm to 50 nm, although lesser and greaterthicknesses can also be employed.

In one embodiment, the effective hexagonal-plane lattice constant of thesecond strain-modulating layer stack 1220 can be greater than theeffective hexagonal-plane lattice constant of the first superlatticeshell 1210, and the effective hexagonal-plane lattice constant of thethird strain-modulating layer stack 1225 can be greater than theeffective hexagonal-plane lattice constant of the secondstrain-modulating layer stack 1220. Further, the atomic concentration ofindium in the second intervening indium gallium nitride layer 1222 canbe greater than the atomic concentration of indium in the firstintervening indium gallium nitride layers 1212, and the atomicconcentration of indium in the third intervening indium gallium nitridelayer 1226 can be greater than the atomic concentration of indium in thesecond intervening indium gallium nitride layer 1222. The atomicpercentage of indium in the second strain-modulating layer stack 1220can be greater than the atomic percentage of indium in the superlatticeshell 1210, and the atomic percentage of indium in the thirdstrain-modulating layer stack 1225 can be greater than the atomicpercentage of indium in the second strain-modulating layer stack 1220.

The superlattice shell 1210 can emit UV radiation, the secondstrain-modulating layer stack 1220 can emit blue visible light and thethird strain-modulating layer stack 1225 can emit green visible light.In one embodiment, the second strain-modulating layer stack 1220 canhave a non-uniform surface profile having at least 3 peaks, where eachof the at least 3 peaks is separated from an adjacent one of the atleast 3 peaks by a valley; and each of the at least 3 peaks extends atleast 2 nm in a radial direction away from an adjacent valley, asdescribed in U.S. Pat. No. 9,281,442, which is incorporated by referenceherein in its entirety. This second strain-modulating layer stack 1220with the non-uniform surface profile can be used for surface profilemodification/preparation of the light emitting region shell 1230 withindium rich regions in addition to strain management.

The light emitting region shell 1230 can be a light-emitting quantumwell which is formed on the most distal strain-modulating layer stack,which can be the third strain-modulating layer stack 1225. The shelllight-emitting quantum well 1230 includes a shell light-emitting indiumgallium nitride layer 1232, a shell aluminum gallium nitride layer 1233,and a shell GaN barrier layer 1234.

The shell light-emitting indium gallium nitride layer 1232 includes anepitaxial indium gallium nitride material having a composition thatemits light at a peak wavelength in a range from 600 nm to 750 nm, andpreferably in a range from 610 nm to 680 nm. In one embodiment, theshell light-emitting indium gallium nitride layer 1232 can have athickness in a range from 3 nm to 7 nm.

In one embodiment, the shell light-emitting indium gallium nitride layer1232 contains indium rich regions having at least 5 atomic percenthigher indium content than indium poor regions in the active regionquantum well shell, which is believed to be at least in part due to thenon-uniform surface profile of the underlying second strain-modulatinglayer stack 1220, as described in U.S. Pat. No. 9,281,442.

The shell aluminum gallium nitride layer 1233 includes a thin aluminumgallium nitride material that can prevent evaporation of indium from theunderlying shell light-emitting indium gallium nitride layer 1232 duringfabrication. The shell aluminum gallium nitride layer 1233 can have acomposition of Al_(y)Ga_((1-y))N, in which y is in a range from 0.3 to1.0 (such as from 0.5 to 0.8). In one embodiment, the shell aluminumgallium nitride layer can have a thickness in a range from 0.2 nm to 3.0nm (such as 0.5 nm to 1.5 nm), such as from 0.5 nm to 1.0 nm.

The shell GaN barrier layer 1234 can have a thickness in a range from 5nm to 20 nm. The shell GaN barrier layer 1234 provides an energy barrierbetween the shell light-emitting indium gallium nitride layer 1232 andp-type compound semiconductor material layers to be subsequently formed.Optionally, one or more of the various strain-modifying layers (1210,1218, 1220, 1225) described above may be omitted and the shelllight-emitting quantum well 1230 may be formed directly on the nanowirecore 32, on a GaN or AlGaN barrier layer, and/or on one of the othershell layers located on the nanowire core 32, due to the nano-compliancyof the nanowire core 32.

The various material layers within the superlattice shell 1210, theshell GaN spacer layer 1218, the second strain-modulating layer stack1220, the third strain-modulating layer stack 1225, and the shelllight-emitting quantum well 1230 can be undoped (e.g., not intentionallydoped), and may have a free charge carrier concentration not greaterthan 1.0×10¹⁹/cm³.

A shell p-doped aluminum gallium nitride layer 1240 can be formed on theshell layer stack 34, i.e., on the shell light-emitting quantum well1230. For example, the shell p-doped aluminum gallium nitride layer 1240can be formed directly on the shell GaN barrier layer 1234. In oneembodiment, the shell p-doped aluminum gallium nitride layer 1240 canhave a thickness in a range from 10 nm to 30 nm, although lesser andgreater thicknesses can also be employed. In one embodiment, the shellp-doped aluminum gallium nitride layer 1240 can be p-doped at a dopantconcentration that provides a free charge carrier concentration (i.e.,the concentration of holes) in a range from 1.0×10¹⁷/cm³ to3.0×10²⁰/cm³, such as from 3.0×10¹⁷/cm³ to 1.0×10²⁰/cm³, although lesserand greater free charge carrier concentrations can also be employed. Theshell p-doped aluminum gallium nitride layer 1240 can have a loweraluminum content than the shell aluminum gallium nitride layer 1233 andcan have a composition of Al_(z)Ga_((1-z))N, in which z is less than0.5, such as in a range from 0.2 to 0.3.

A first p-doped compound semiconductor material layer 1250 can be formedon the shell stack 34 (e.g., on the shell p-doped aluminum galliumnitride layer 1240 which forms the outer surface of the shell stack 34).The first p-doped compound semiconductor material layer 1250 can includea p-doped single crystalline compound semiconductor material such asp-doped gallium nitride. In one embodiment, the first p-doped compoundsemiconductor material layer 1250 can be p-doped at a dopantconcentration that provides a free charge carrier concentration (i.e.,the concentration of holes) in a range from 1.0×10¹⁷/cm³ to3.0×10²⁰/cm³, such as from 3.0×10¹⁷/cm³ to 1.0×10²⁰/cm³, although lesserand greater free charge carrier concentrations can also be employed. Thedeposited p-doped compound semiconductor material coalesces between thenanowires, with or without vertical seams or voids laterally surroundingeach nanowire, to form the first p-doped compound semiconductor materiallayer 1250 as a continuous material layer.

Each combination of a nanowires core 32, a shell layer stack 34, a shellp-doped aluminum gallium nitride layer 1240, and a first p-dopedcompound semiconductor material layer 1250 constitutes a semiconductornanowire 1300.

A second p-doped compound semiconductor material layer 1260 can beformed on the first p-doped compound semiconductor material layer 1250.The second p-doped compound semiconductor material layer 1260 caninclude a p-doped single crystalline compound semiconductor materialsuch as p-doped gallium nitride. The dopant concentration in the secondp-doped compound semiconductor material layer 1260 can be greater thanthe dopant concentration in the first p-doped compound semiconductormaterial layer 1250. In one embodiment, the second p-doped compoundsemiconductor material layer 1260 can be p-doped at a dopantconcentration that provides a free charge carrier concentration (i.e.,the concentration of holes) in a range from 5.0×10¹⁹/cm³ to3.0×10²¹/cm³, such as from 1.0×10²⁰/cm³ to 2.0×10²¹/cm³, although lesserand greater free charge carrier concentrations can also be employed. Thethickness of the second p-doped compound semiconductor material layer1260 is selected such that the second p-doped compound semiconductormaterial layer 1260 is either formed as a continuous material layerfilling the gaps between the semiconductor nanowires 1300 and providinga continuous top surface or forms an air-bridge structure enclosing airgaps between the semiconductor nanowires, as described in U.S. Pat. No.8,350,249, incorporated herein by reference in its entirety.

Top electrodes 30 can be formed on the light emitting diodes 20. Thearea of each light emitting diode 20 can be defined by the area of arespective one of the top electrodes 20. In one embodiment, each topelectrode 30 can include a vertical stack of a transparent conductiveelectrode and a patterned portion of a reflector layer 966.

The transparent conductive electrodes can be formed by depositing andpatterning a transparent conductive oxide layer 964 over the first andsecond p-doped compound semiconductor material layers (1150, 1160). Incase light emitted from the light emitting diodes 20 is directeddownward toward the substrate 10 by a reflector layer to be subsequentlyformed above the transparent conductive electrode, then the transparentconductive oxide layer 964 is herein referred to a backside transparentconductive oxide layer 964. The transparent conductive oxide layer 964includes a transparent conductive oxide material such as indium tinoxide or aluminum doped zinc oxide. The transparent conductive oxidelayer 964 can be deposited as a continuous material layer that extendsacross the entire area of the p-doped compound semiconductor materiallayer 812. The thickness of the transparent conductive oxide layer 964can be in a range from 100 nm to 2 microns, such as from 200 nm to 1micron, although lesser and greater thicknesses can also be employed.

Optionally, a reflector material can be deposited to form a reflectorlayer 966 that continuously extends over the backside transparentconductive oxide layer 964. The reflector layer 966 is electricallyshorted to the p-doped compound semiconductor material layer 1160through the backside transparent conductive oxide layer 964. In oneembodiment, the reflector layer 966 includes at least one materialselected from silver, aluminum, copper, and gold. In one embodiment, thereflector material can be deposited by physical vapor deposition(sputtering) or vacuum evaporation. The reflector layer 966 can beemployed to reflect light emitted from the active region 1130 throughthe transparent substrate 10. In case the reflector layer 966 isdeposited and patterned to be incorporated into top electrodes (964,966), the area of each patterned portion of the reflector layer 966defines the areas of a respective light emitting diode. Each lightemitting diode 20 can be in a downward-emitting configuration, i.e., aconfiguration in which light exits the light emitting diodes through thesubstrate 10, which can include a transparent material.

While exemplary configurations of non-planar light emitting diodes areillustrated for illustrative purposes, the present invention can bepracticed with any other non-planar light emitting diodes that areformed on a substrate 10.

The substrate 10 can be an epitaxial substrate, and at least one lightemitting diode 20 can be formed on the substrate. Each light emittingdiode 20 can include an n-doped semiconductor material layer, alight-emitting active region, and a p-doped semiconductor materiallayer. In one embodiment, each light-emitting active region can comprisean epitaxial semiconductor material in epitaxial alignment with theepitaxial substrate.

Referring to FIG. 2, at least one dielectric isolation layer 40 can beformed on the light emitting diodes 20 and the top electrodes 30. The atleast one dielectric isolation layer 40 can include a single dielectricmaterial layer, or can include a plurality of dielectric materiallayers. The at least one dielectric isolation layer 40 can include atleast one amorphous dielectric material layer. The at least onedielectric isolation layer 40 can include silicon oxide, siliconnitride, and/or at least one dielectric oxide material (such as aluminumoxide). Optionally, the topmost surface of the at least one dielectricisolation layer 40 can be planarized, for example, by chemicalmechanical planarization. The thickness of the at least one dielectricisolation layer 40 above the top electrodes 30 can be in a range from0.2 microns to 10 microns, such as from 0.4 microns to 5 microns,although lesser and greater thicknesses can also be employed.

An indium gallium zinc oxide (IGZO) layer 50L can be formed on the topsurface of the at least one dielectric isolation layer 50L. IGZO has ahigh electron mobility that is about 20-50 L times the electron mobilityof amorphous silicon, and can be employed as the channel material forfield effect transistors having high switching speeds. IGZO has auniform amorphous phase, and can be deposited by pulsed laser deposition(PLD). In a PLD process, a laser can be employed to focus on nano-sizedspots on solid elemental targets. Laser pulse frequencies are variedbetween the targets in ratios to control the composition of the film.The deposition chamber can be in a vacuum environment with a residualoxygen pressure, which can be employed to improve electrical propertiesof the deposited IGZO material. Alternatively, spin-coating may beemployed in lieu of a PLD process to deposit the IGZO material. Thethickness of the IGZO layer 50L may be in a range from 30 nm to 300 nm,although lesser and greater thicknesses can also be employed.

Referring to FIG. 3, the IGZO layer 50L can be patterned into discreteportions, for example, by application and patterning of a photoresistlayer over the IGZO layer 50L, and by an etch process that transfers thepattern in the photoresist layer through the IGZO layer 50L. Ananisotropic etch or an isotropic etch can be employed to pattern theIGZO layer 50L. Each patterned portion of the IGZO layer 50L constitutesan IGZO channel 50, which is a channel region of an IGZO field effecttransistor to be subsequently formed. The photoresist layer can besubsequently removed, for example, by ashing.

A gate dielectric layer 60L is formed on the physically exposed surfacesof the at least one dielectric isolation layer 40 and the IGZO channels50. The gate dielectric layer 60L may be formed as a continuous materiallayer. The gate dielectric layer 60L may include a single dielectricmaterial layer or may include a stack of multiple dielectric materiallayers. The gate dielectric layer 60L includes a gate dielectricmaterial such as silicon oxide, silicon oxynitride, at least onedielectric metal oxide material, or a combination or a stack thereof.The thickness of the gate dielectric layer 60L can be in a range from 1nm to 12 nm, such as from 2 nm to 6 nm, although lesser and greaterthicknesses can also be employed. In one embodiment, the gate dielectriclayer 60L may be formed as a conformal dielectric material layer.

Referring to FIG. 4, a pair of openings is formed through each region ofthe gate dielectric layer 60L that overlies an IGZO channel 50. Thelocations of the openings are selected such that an intervening area forforming a gate electrode 66 is provided between each pair of openings onthe IGZO channels 50. For example, a photoresist layer (not shown) canbe applied over the gate dielectric layer 60L, and can belithographically patterned by a first lithographic exposure process anda first lithographic development process to form a pair of openingsabove each IGZO channel 50. An etch process is performed to formopenings through the gate dielectric layer 60L underneath each openingin the photoresist layer. Additional patterns of openings can be formedthrough the photoresist layer by a second lithographic exposure processand a second lithographic development process to form openings withinareas in which gate electrodes 66 are to be subsequently formed.

At least one conductive material can be deposited in the openingsthrough the photoresist layer to form a source electrode 62, a drainelectrode 64, and a gate electrode 66 on each of the IGZO channels 50.The at least one conductive material can include at least one metallicmaterial (such as TiN, TaN, WN, Ti, Ta, W, or combinations of thereof)and/or at least one heavily doped semiconductor material. Excessportions of the at least one conductive material over the photoresistlayer may be removed, for example, by a lift-off process.

Field effect transistors comprising a respective indium gallium zincoxide (IGZO) channel 50 are formed on the at least one dielectricisolation layer 40. Each IGZO channel 50 can be located above a topsurface of the at least one dielectric isolation layer 40. Each fieldeffect transistor comprises a gate dielectric (which is a portion of thegate dielectric layer 60L that contacts the IGZO channel 50) contactinga top surface of the IGZO channel 50. A gate electrode 66 of each fieldeffect transistor overlies the gate dielectric of the field effecttransistor.

Referring to FIG. 5, interconnect-level dielectric layer (70, 80, 90)and metal interconnect structures (71, 72, 74, 76, 82, 84, 86, 88. 92)can be formed over the field effect transistors (50, 60, 62, 64, 66). Anelectrically conductive path (71, 74, 84) that electrically shorts anode of a light emitting diode 20 to a node of a field effect transistor(50, 60, 62, 64, 66) can be formed for each pair of a light emittingdiode 20 and a field effect transistor (50, 60, 62, 64, 66) having anareal overlap in a plan view. As used herein, a plan view refers to aview along the vertical direction in which layout of the various lightemitting diodes 20 and the field effect transistors (50, 60, 62, 64, 66)are shown.

Each electrically conductive path (71, 74, 84) can include e a contactvia structure 71 that extends through the at least one dielectricisolation layer 40, a conductive line structure 84 that contacts a topsurface of the contact via structure 71 and located over a field effecttransistor (50, 60, 62, 64, 66), and an active region contact viastructure 74 that contacts a source electrode 62 or a drain electrode 64of the field effect transistor (50, 60, 62, 64, 66). In one embodiment,the light emitting diode 20 comprises a top electrode 30 contacting atop surface of the p-doped semiconductor material layer (1250, 1260) andcontacting a bottom surface of the contact via structure 71. In oneembodiment, the node of the field effect transistor (50, 60, 62, 64, 66)that is electrically shorted to the electrically conductive path (71,74, 84) comprises a source region 62 or a drain region 64 of the fieldeffect transistor (50, 60, 62, 64, 66).

The interconnect-level dielectric layer (70, 80, 90) can include acontact-level dielectric layer 70 embedding contact via structures (71,72, 74, 76), a first interconnection-level dielectric layer 80 thatoverlies the contact-level dielectric layer 70 and embeds first-levelconductive line structures (82, 84, 86) and first-level interconnect viastructures 88, and a second interconnect-level dielectric layer 90 thatoverlies the first interconnect-level dielectric layer 80 and embeddingsecond-level conductive line structures 92. The contact via structures(71, 72, 74, 76) can include top electrode contact via structures 71that contact a respective top electrode 30 of the light emitting diodes20, source contact via structures 72 that contact a respective sourceelectrode 62 of the field effect transistors (50, 60, 62, 64, 66), draincontact via structures 74 that contact a respective drain electrode 64of the field effect transistors (50, 60, 62, 64, 66), and gate contactvia structures 76 that contact a respective drain electrode 66 of thefield effect transistors (50, 60, 62, 64, 66). The first-levelconductive line structures (82, 84, 86) can include diode-transistorinterconnection lines 84 that contact a respective pair of a topelectrode contact via structures 71 and a drain contact via structure 74or a respective pair of a top electrode contact via structure 71 and asource contact via structure 72. The first-level conductive linestructures (82, 84, 86) can further include gate interconnection linestructures 86 that contact a respective one of the gate contact viastructures 76, and transistor active region interconnect lines 82 thatcontact a respective one of the source contact via structures 72 anddrain contact via structures 74. The first-level interconnect viastructures 88 can contact a top surface of a respective one of thetransistor active region interconnect lines 82. The second-levelconductive line structures 92 can contact a top surface of a respectiveone of the first-level interconnect via structures 88.

All, or some, of the metal interconnect structures (71, 72, 74, 76, 82,84, 86, 88. 92) can be formed by forming openings in a respective one ofthe interconnect-level dielectric layer (70, 80, 90) and by filling theopenings with at least one conductive material, which can include, forexample, a metallic liner 71A that includes a metallic barrier materialsuch as TiN, TaN, and/or WN and a metallic fill material portion 71Bthat includes a metallic fill material such as Ti, Ta, W, Cu, Co, Ru,Mo, Al, or combinations thereof. All or some of the first-levelconductive line structures (82, 84, 86) and the second-level conductiveline structures 92 may be formed by depositing at least one metallicmaterial and by patterning the at least one metallic material.

Referring to FIG. 6, an alternative configuration of the first exemplarystructure is illustrated after formation of gate electrodes 66 and agate dielectric layer 60L. In the alternative configuration, the gateelectrodes 66 of the field effect transistors can be formed by formingdiscrete recessed regions at the top surface of the at least onedielectric isolation layer 40. The discrete recessed regions can beformed, for example, by applying and lithographically patterning aphotoresist layer over the at least one dielectric isolation layer 40 toform openings through the photoresist layer, and by transferring thepattern of the openings in the photoresist layer into an upper portionof the at least one dielectric isolation layer 40 employing ananisotropic etch or an isotropic etch. The photoresist layer can besubsequently removed, for example, by ashing. At least one conductivematerial (which may include a doped semiconductor material and/or ametallic material) can be deposited in the discrete recessed regions,and excess portions of the at least one conductive material can beremoved from the top surface of the at least one dielectric isolationlayer 40 by a planarization process, such as chemical mechanicalplanarization or a recess etch. Each remaining portion of the at leastone conductive material in the discrete recessed regions constitutes agate electrode 66. Alternatively, the gate electrodes 66 may be formedby depositing at least one conductive material over the at least onedielectric isolation layer, and by patterning the at least oneconductive material into discrete conductive material portions. Eachpatterned discrete conductive material portion can constitute a gateelectrode 66.

A gate dielectric layer 60L can be formed over the gate electrodes 66and the at least one dielectric spacer layer 40 by deposition of atleast one gate dielectric material. In an alternative configurationillustrated in FIG. 6, a gate electrode 66 of each field effecttransistor may be embedded within a top portion of, or located over, theat least one dielectric isolation layer 40. A gate dielectric (i.e., aportion of the gate dielectric layer 60L that subsequently contacts arespective IGZO channel to be subsequently formed) of each field effecttransistor overlies the gate electrode 66 and the at least onedielectric isolation layer 40.

Referring to FIG. 7, IGZO channels 50 are formed on a top surface of thegate dielectric layer 60L by deposition and patterning of the IGZOmaterial. The IGZO channels 50 can be formed as discrete materialportions that do not contact one another. A contact-level dielectriclayer 70 is formed over the IGZO channels 50 by deposition of adielectric material. A pair of openings can be formed through eachregion of the contact-level dielectric layer 70 that overlies arespective IGZO channel 50. The locations of the openings are selectedsuch that a gate electrode 66 underlies the space between each pair ofopenings on the IGZO channels 50. For example, a photoresist layer (notshown) can be applied over the gate dielectric layer 60L, and can belithographically patterned by a lithographic exposure process and alithographic development process to form a pair of openings above eachIGZO channel 50. Two openings laterally offset from an underlying gateelectrode 66 is formed per IGZO channel 50.

At least one conductive material can be deposited in the openingsthrough the photoresist layer to form a source electrode 62 and a drainelectrode 64 on each of the IGZO channels 50. The at least oneconductive material can include at least one metallic material (such asTiN, TaN, WN, Ti, Ta, W, or combinations of thereof) and/or at least oneheavily doped semiconductor material. Excess portions of the at leastone conductive material over the photoresist layer may be removed, forexample, by a lift-off process that removes the photoresist layer.

Field effect transistors comprising a respective indium gallium zincoxide (IGZO) channel 50 are formed on, and over, the at least onedielectric isolation layer 40. Each IGZO channel 50 can be located abovea top surface of the gate dielectric layer 60L, which is located abovethe at least one dielectric isolation layer 40. Each field effecttransistor comprises a gate dielectric (which is a portion of the gatedielectric layer 60L that contacts the IGZO channel 50) contacting abottom surface of the IGZO channel 50. A gate electrode 66 of each fieldeffect transistor underlies the gate dielectric of the field effecttransistor.

Interconnect-level dielectric layer (70, 80, 90) and metal interconnectstructures (71, 72, 74, 76, 82, 84, 86, 88. 92) can be formed over thefield effect transistors (50, 60, 62, 64, 66). The same processing stepscan be employed as the processing steps employed to form theinterconnect-level dielectric layer (70, 80, 90) and metal interconnectstructures (71, 72, 74, 76, 82, 84, 86, 88. 92) of FIG. 5. Anelectrically conductive path (71, 74, 84) that electrically shorts anode of a light emitting diode 20 to a node of a field effect transistor(50, 60, 62, 64, 66) can be formed for each pair of a light emittingdiode 20 and a field effect transistor (50, 60, 62, 64, 66) having anareal overlap in a plan view. Locations of gate contact via structures76 (not shown in FIG. 7) can be selected to avoid contact with the IGZOchannels 50 and to provide electrical contact with the gate electrodes66.

Referring to FIG. 8, a second exemplary structure according to a secondembodiment of the present disclosure is illustrated after formation of ahigh-electron-mobility transistor (HEMT) body layer stack 120 on asubstrate 10, which may be an epitaxial substrate. The HEMT body layerstack 120 may be any heterogeneous semiconductor material stack known inthe art that can provide a two-dimensional electron gas layer that canbe employed to form a HEMT device. In one embodiment, each materiallayer within the HEMT body layer stack 120 can include an epitaxialsemiconductor material layer in epitaxial alignment with the singlecrystalline material within the substrate 10.

In an illustrative example, the HEMT body layer stack 120 can include,from bottom to top, an epitaxial buffer semiconductor layer 122, anepitaxial semiconductor channel layer 124, and a Schottky barriersemiconductor layer 126. The substrate 10 can include single crystallinealuminum oxide, single crystalline silicon carbide, or singlecrystalline InP. The epitaxial buffer semiconductor layer 122 can besingle crystalline GaN or single crystalline InAlAs, and can beepitaxially aligned to the single crystalline structure of the substrate10. The thickness of the epitaxial buffer semiconductor layer 122 can bein a range from 0.5 micron to 5 microns, although lesser and greaterthicknesses can also be employed. The epitaxial semiconductor channellayer 124 can include GaN or InGaAs. The thickness of the epitaxialsemiconductor channel layer 124 can be in a range from 0.5 micron to 5microns, although lesser and greater thicknesses can also be employed.The Schottky barrier semiconductor layer 126 can include an AlGaN singlecrystalline material or an InAlAs single crystalline material. Thethickness of the Schottky barrier semiconductor layer 126 can be in arange from 10 nm to 60 nm, although lesser and greater thicknesses canalso be employed. Optionally, the Schottky barrier semiconductor layer126 can include silicon in a δ-doping layer, i.e., as a thin layerhaving a high concentration of silicon. In some embodiments, theSchottky barrier semiconductor layer 126 can include a stack including,from bottom to top, an undoped AlGaAs spacer and an n-doped AlGaAslayer. Each of the layers within the HEMT body layer stack 120 can beepitaxially aligned to the epitaxial material within the substrate 10.Generally, any semiconductor material layer stack known to provide ahigh mobility electron gas layer can be employed to form the HEMT bodylayer stack 120.

Referring to FIG. 9, gate electrodes 136, source electrodes 132, anddrain electrodes 134 are formed for the HEMT devices. The gateelectrodes 136 can be formed, for example, by applying and patterning aphotoresist layer over the HEMT body layer stack 120 to form a patternof openings having the shapes of gate electrodes 136 to be formed. Ametal stack that provides a Schottky barrier is deposited in theopenings in the photoresist layer. For example, the metal stack caninclude a stack of a platinum layer, a titanium layer, a platinum layer,and a gold layer or a stack of a titanium layer, an aluminum layer, anda titanium layer. The photoresist layer and portions of the metal stackthat overlie the photoresist layer can be lifted off. The remainingportion of the metal stack constitute the gate electrodes 136.

Another photoresist layer can be applied and patterned over the HEMTbody layer stack 120 to form a pattern of openings having the shapes ofsource electrodes 132 and drain electrodes 134 to be formed. A metalstack that provides an Ohmic contact can be deposited in the openingsthrough the photoresist layer on the HEMT body layer stack 120. Forexample, the metal stack can include a stack of a titanium layer, analuminum layer, a titanium layer, and a gold layer, or a stack of atitanium layer, an aluminum layer, a molybdenum layer, and a gold layer.The photoresist layer and portions of the metal stack that overlie thephotoresist layer can be lifted off. Remaining portions of the metalstack constitute the source electrodes 132 and the drain electrodes 134.High-electron-mobility transistor (HEMT) devices comprising an epitaxialsemiconductor channel layer 124 are formed over the substrate 10, whichcan be an epitaxial substrate.

Referring to FIG. 10, at least one isolation layer 140 is formed overthe HEMT devices. The at least one isolation layer 140 provideselectrical isolation between the HEMT devices and devices to besubsequently formed over the at least one isolation layer 140. In oneembodiment, the at least one isolation layer 140 can include, frombottom to top, a lower crystalline graded composition layer 142, acrystalline electrically insulating layer 144, and an upper crystallinegraded composition layer 146.

The lower crystalline graded composition layer 142 can have a verticalcompositional gradient such that the lattice constant at the bottom ofthe lower crystalline graded composition layer 142 substantially matchesthe lattice constant of the Schottky barrier semiconductor layer 126 andthe lattice constant at the top of the lower crystalline gradedcomposition layer 142 substantially matches the lattice constant of thecrystalline electrically insulating layer 144. For example, the lowercrystalline graded composition layer 142 can be a graded AlGaN layer inwhich the atomic concentration of aluminum increases with the distancefrom the substrate 10. The thickness of the lower crystalline gradedcomposition layer 142 can be in a range from 0.2 micron to 4 microns,although lesser and greater thicknesses can also be employed. The lowercrystalline graded composition layer 142 can be formed by a selective ornon-selective epitaxial deposition process. In one embodiment, aselective epitaxial deposition process can be employed to form the lowercrystalline graded composition layer 142, and the lower crystallinegraded composition layer 142 can grow over the gate electrodes 136, thesource electrodes 132, and the drain electrodes 134 of the HEMT devices.The overgrown portions of the lower crystalline graded composition layer142 can merge above the gate electrodes 136, the source electrodes 132,and the drain electrodes 134 such that the top portion of the lowercrystalline graded composition layer 142 can be single crystalline withdislocations over the areas of the gate electrodes 136, the sourceelectrodes 132, and the drain electrodes 134, or may include largegrains having a same set of crystallographic orientations and grainboundaries therebetween.

The ratio of the total physically exposed area of the HEMT body layerstack 126 to the total area covered by the gate electrodes 136, thesource electrodes 132, and the drain electrodes 134 can be maintained ina range that allows epitaxial alignment of a predominant portion (suchas more than 50% in volume) of the at least one isolation layer 140 tothe epitaxial material layers within the HEMT body layer stack 120. Forexample, the ratio of the total physically exposed area of the HEMT bodylayer stack 126 to the total area covered by the gate electrodes 136,the source electrodes 132, and the drain electrodes 134 can be in arange from 1:2 to 10:1 such as from 1:1 to 3:1, although lesser andgreater ratios can also be employed. Optionally, thin dielectric liners(not shown) may be formed to cover the gate electrodes 136, the sourceelectrodes 132, and the drain electrodes 134, and to suppress epitaxialgrowth of the material(s) of the at least one isolation layer 140, whileenabling growth of the epitaxial material(s) of the at least oneisolation layer 140 from the physically exposed surfaces of the HEMTbody layer stack 120.

The crystalline electrically insulating layer 144 includes anelectrically insulating crystalline material such as AlN. The thicknessof the crystalline electrically insulating layer 144 can be in a rangefrom 1 nm to 100 nm, although lesser and greater thicknesses can also beemployed. The crystalline electrically insulating layer 144 can besubstantially single crystalline, or may have large grain sizes with asame set of crystallographic orientations and grain boundariestherebetween.

The upper crystalline graded composition layer 146 can have a verticalcompositional gradient such that the lattice constant at the bottom ofthe upper crystalline graded composition layer 146 substantially matchesthe lattice constant of the crystalline electrically insulating layer144 and the lattice constant at the top of the upper crystalline gradedcomposition layer 146 substantially matches the lattice constant of asingle crystalline semiconductor material layer to be subsequentlyformed thereabove. For example, the single crystalline semiconductormaterial layer to be subsequently formed can include a first singlecrystalline n-doped gallium nitride layer 804 described above. In oneembodiment, the upper crystalline graded composition layer 146 can be agraded AlGaN layer in which the atomic concentration of aluminumdecreases with the distance from the substrate 10. The thickness of theupper crystalline graded composition layer 146 can be in a range from0.2 micron to 4 microns, although lesser and greater thicknesses canalso be employed.

In one embodiment, the aluminum concentration in the upper region of thelower crystalline graded composition layer 142 and/or the lower regionof the upper crystalline graded composition layer 146 can be high enoughthat the upper region of the lower crystalline graded composition layer142 and/or the lower region of the upper crystalline graded compositionlayer 146 constitute electrically insulating layers. In this case, thecrystalline electrically insulating layer 144 may be omitted, and theupper region of the lower crystalline graded composition layer 142and/or the lower region of the upper crystalline graded compositionlayer 146 can provide electrical isolation along a vertical direction.Generally, the at least one isolation layer 140 includes at least oneelectrically insulating layer in the form of a crystalline electricallyinsulating layer 144, an upper region of the lower crystalline gradedcomposition layer 142, and/or a lower region of the upper crystallinegraded composition layer 146. The at least one isolation layer 140,including the at least one electrically insulating layer, includes atleast one epitaxial dielectric material in epitaxial alignment with theepitaxial semiconductor channel layer 124.

In one embodiment, the lower crystalline graded composition layer 142can be embodied as a first graded aluminum gallium nitride layer inwhich an atomic concentration of aluminum increases with a verticaldistance from the epitaxial substrate, the crystalline electricallyinsulating layer 144 can be embodied as an aluminum nitride layerlocated on the first graded aluminum gallium nitride layer and includingaluminum nitride as the epitaxial dielectric material, and the uppercrystalline graded composition layer 146 can be embodied as a secondgraded aluminum gallium nitride layer in which an atomic concentrationof aluminum decreases with a vertical distance from the epitaxialsubstrate.

Referring to FIGS. 11 and 1B-1E, light emitting diodes 20 and topelectrodes 30 can be formed in the same manner as in the firstembodiment. Any of the configurations described above can be employed toform the light emitting diodes 20 and the top electrodes 30. Generally,a light emitting diode 20 comprises an n-doped semiconductor materiallayer (such as a first single crystalline n-doped gallium nitride layer804), a light-emitting active region, 1130 and a p-doped semiconductormaterial layer (1250, 1260). The light-emitting active region 30comprises an epitaxial semiconductor material in epitaxial alignmentwith the at least one isolation layer 140 and with the HEMT body layerstack 120 and with the epitaxial material in the substrate 10.

Referring to FIGS. 12A and 12B, interconnect-level dielectric layers(170, 190) and metal interconnect structures (171, 182, 173, 192, 196)can be formed over the light emitting diodes 20 and the top electrodes30. The light emitting diodes 20 can overlie, and can have an arealoverlap in a plan view with, a respective HEMT (120, 132, 134, 136). Inone embodiment, an electrically conductive path (171, 192, 173) thatelectrically shorts a node of the light emitting diode 20 to a node ofthe HEMT (120, 132, 134, 136) for each vertically neighboring pair of alight emitting diode 20 and an HEMT (120, 132, 134, 136). In oneembodiment, the electrically conductive path (171, 192, 173) comprises acontact via structure (which is herein referred to as HEMT contact viastructure 171) that extends through the at least one isolation layer140, a conductive line structure (which is herein referred to as adiode-transistor interconnection line 192) that contacts a top surfaceof the HEMT contact via structure 171 and located above a top surface ofthe at least one isolation layer 140, and a first diode contact viastructure 173 that contacts a bottom electrode (such as a first singlecrystalline n-doped gallium nitride layer 804) or a top electrode 30 ofthe light emitting diode 20. In an embodiment, a bottom surface of theHEMT contact via structure 171 can contact a drain electrode 134 of theHEMT (120, 132, 134, 136) as shown in FIG. 12B. In another embodiment, abottom surface of the HEMT contact via structure 171 can contact asource electrode 132 of the HEMT (120, 132, 134, 136) (not shown).Dielectric liners 161 can be provided to provide lateral electricalisolation to all, or some, of the contact via structures (171, 172,173).

The interconnect-level dielectric layer (170, 190) can include acontact-level dielectric layer 170 embedding contact via structures(171, 172, 173) and an interconnection-level dielectric layer 190 thatoverlies the contact-level dielectric layer 170 and embeds conductiveline structures (192, 196). The contact via structures (171, 172, 173)can include the HEMT contact via structures 171 that contact a node of arespective HEMT (120, 132, 134, 136), top contact via structures 173that contact a respective top electrode 30 of the light emitting diodes20, and bottom contact via structures 172 that contact a respectivebottom electrode (such as a first single crystalline n-doped galliumnitride layer 804) of the light emitting diodes 20. The conductive linestructures (192, 196) can include diode-transistor interconnection lines192 that contact a respective pair of an HEMT contact via structures 171contacting an HEMT and one of a top electrode contact via structure 173and a bottom electrode contact via structure 172 that are connected toan overlying light emitting diode 20. The conductive line structures(192, 196) include diode interconnection line structures 196. Each diodeinterconnection line structure 196 can contact another of the topelectrode contact via structure 173 and the bottom electrode contact viastructure 172 connected to a light emitting diode 20 that overlies anHEMT.

All or some of the metal interconnect structures (171, 172, 173, 192,196) can be formed by forming openings in a respective one of theinterconnect-level dielectric layer (170, 190) and by filling theopenings with at least one conductive material, which can include, forexample, a metallic liner 71A that includes a metallic barrier materialsuch as TiN, TaN, and/or WN and a metallic fill material portion 71Bthat includes a metallic fill material such as Ti, Ta, W, Cu, Co, Ru,Mo, Al, or combinations thereof. In this case, a dielectric liner 161can laterally surround each conductive via structure (171, 172, 173) andcan vertically extend through each of the at least one isolation layer140. All or some of the conductive line structures (192, 196) may beformed by depositing at least one metallic material and by patterningthe at least one metallic material.

Referring to all embodiments of the present disclosure, each of thematerial layers within the light emitting diodes 20 can be singlecrystalline epitaxial material layers with the exception of the growthmask 42 in the third configuration illustrated in FIGS. 1D and 1E. Assuch, the active regions 1130 or the light emitting region shells 1230of the light emitting diodes 20 can be single crystalline, and canprovide effective emission of light. By providing control transistorsabove or below light emitting diodes 20, the need to transfer any lightemitting diode 20 to a backplane is eliminated. Light emitting diodes 20emitting light at different peak wavelengths can be formed on the samesubstrate 10 by masking various areas of the device area with temporaryor permanent masking material layers and/or by altering materialcompositions of the active regions 1130 or the light emitting regionshells 1230 across the various device areas, thereby forming an array ofpixels including multiple sub-pixels emitting light at different peakwavelengths (such as at a red color, at a green color, and at a bluecolor). A direct view display device including built-in controltransistors can be formed without transferring any light emitting diode.The control transistors may be IGZO transistors including a respectiveIGZO channel, or may be a HEMT transistor including a respective regionof a two-dimensional electron gas layer.

Although the foregoing refers to particular preferred embodiments, itwill be understood that the invention is not so limited. It will occurto those of ordinary skill in the art that various modifications may bemade to the disclosed embodiments and that such modifications areintended to be within the scope of the invention. Where an embodimentemploying a particular structure and/or configuration is illustrated inthe present disclosure, it is understood that the present invention maybe practiced with any other compatible structures and/or configurationsthat are functionally equivalent provided that such substitutions arenot explicitly forbidden or otherwise known to be impossible to one ofordinary skill in the art.

What is claimed is:
 1. A light emitting device, comprising: an epitaxialsubstrate; a high-electron-mobility transistor (HEMT) located on theepitaxial substrate and comprising an epitaxial semiconductor channellayer; at least one isolation layer located over the HEMT; a lightemitting diode comprising an n-doped semiconductor material layer, alight-emitting active region, and a p-doped semiconductor materiallayer, wherein the light-emitting active region comprises an epitaxialsemiconductor material in epitaxial alignment with the at least oneisolation layer; and an electrically conductive path that electricallyshorts a node of the light emitting diode to a node of the HEMT, whereinthe HEMT and the light emitting diode have an areal overlap in a planview, wherein the at least one isolation layer comprises an epitaxialdielectric material in epitaxial alignment with the epitaxialsemiconductor channel layer, and wherein the at least one isolationlayer comprises a layer stack including, from bottom to top: a firstgraded aluminum gallium nitride layer in which an atomic concentrationof aluminum increases with a vertical distance from the epitaxialsubstrate; an aluminum nitride layer located on the first gradedaluminum gallium nitride layer and including aluminum nitride as theepitaxial dielectric material; and a second graded aluminum galliumnitride layer in which an atomic concentration of aluminum decreaseswith a vertical distance from the epitaxial substrate.
 2. The lightemitting device of claim 1, wherein the electrically conductive pathcomprises a contact via structure that extends through the at least oneisolation layer.
 3. The light emitting device of claim 2, wherein theelectrically conductive path further comprises a conductive linestructure that is located above a top surface of the at least oneisolation layer and contacts a top surface of the contact via structure.4. The light emitting device of claim 2, wherein a bottom surface of thecontact via structure contacts a source electrode of the HEMT or a drainelectrode of the HEMT.
 5. The light emitting device of claim 2, furthercomprising a dielectric liner laterally surrounding the conductive viastructure and extending through each of the at least one isolationlayer.
 6. A light emitting device, comprising: an epitaxial substrate; ahigh-electron-mobility transistor (HEMT) located on the epitaxialsubstrate and comprising an epitaxial semiconductor channel layer; atleast one isolation layer located over the HEMT; a light emitting diodecomprising an n-doped semiconductor material layer, a light-emittingactive region, and a p-doped semiconductor material layer, wherein thelight-emitting active region comprises an epitaxial semiconductormaterial in epitaxial alignment with the at least one isolation layer;and an electrically conductive path that electrically shorts a node ofthe light emitting diode to a node of the HEMT, wherein the at least oneisolation layer comprises an epitaxial dielectric material in epitaxialalignment with the epitaxial semiconductor channel layer; and whereinthe at least one isolation layer comprises a layer stack including, frombottom to top: a first graded aluminum gallium nitride layer in which anatomic concentration of aluminum increases with a vertical distance fromthe epitaxial substrate; an aluminum nitride layer located on the firstgraded aluminum gallium nitride layer and including aluminum nitride asthe epitaxial dielectric material; and a second graded aluminum galliumnitride layer in which an atomic concentration of aluminum decreaseswith a vertical distance from the epitaxial substrate.